Add more details

Add more explainations on the purpose of the functions, make it more general for global data persistence, so it is not specific for global query parameter
Signed-off-by: abbyhu2000 <abigailhu2000@gmail.com>

src/plugins/opensearch_dashboards_utils/docs/global_query_param.md

@@ -1,13 +1,14 @@
-# Global query parameters
+# Global data persistence
 
-As of 12/1/2022, there are five plugins that have implemented global data persistence ability in OpenSearch Dashboards, and they are visualize, discover, Timeline, dashboards, and vis-builder. Global query parameters include globally pinned filters, time range and time refresh intervals. These parameters are not only persisted across the action of refresh, but also persisted among all the plugins that have global data persistence ability. 
+As of 12/1/2022, there are five plugins that have implemented global data persistence ability in OpenSearch Dashboards, and they are visualize, discover, Timeline, dashboards, and vis-builder. Global data persistence means that the data are not only persisted over refreshes, but also able to be persisted across multiple plugins. We utilize [state containers](https://github.com/opensearch-project/OpenSearch-Dashboards/tree/main/src/plugins/opensearch_dashboards_utils/docs/state_containers), [state storage](https://github.com/opensearch-project/OpenSearch-Dashboards/tree/main/src/plugins/opensearch_dashboards_utils/docs/state_sync/storages) and [state syncing utilities](https://github.com/opensearch-project/OpenSearch-Dashboards/tree/main/src/plugins/opensearch_dashboards_utils/docs/state_sync) from [OpenSearch Dashboards Utils](https://github.com/opensearch-project/OpenSearch-Dashboards/tree/main/src/plugins/opensearch_dashboards_utils) to achieve global data persistence. User can choose to persist data either in URL or session storage by changing the setting `Store URLs in session storage` under advanced setting page.
 
-For example, we set a specific time range and time refresh interval when trying to a new visualization. When we navigate to the dashboard page, we can see the previous time range and time refresh interval that are set within the visualization app are still there. However, when we create a filter, it will only be persisted within that specific plugin since it is not a global filter. We can make a filter become a global filter by selecting 
-`Pin across all apps`. Only global filters are persisted across all other globally persistent plugins within the application.
+One of the global data persistence example that currently exists is global query parameters. Global query parameters include globally pinned filters, time range and time refresh intervals. For example, we set a specific time range and time refresh interval when trying to a new visualization. When we navigate to the dashboard page, we can see the previous time range and time refresh interval that are set within the visualization app are still there. However, when we create a filter, it will only be persisted within that specific plugin since it is not a global filter. We can make a filter become a global filter by selecting `Pin across all apps`. Only global filters are persisted across all other globally persistent plugins within the application. 
+
+The following five steps demonstrate how to add global query parameter persistence for a plugin. Step 3 and 4 are specific to global query parameter persistence. For implementing global data persistence in general, step 1 and 2 are required. A function that is similar to step 3 to sync up the state manager of the data with osdUrlStateStorage is also required.
 
 # Steps to add global data persistence ability to a plugin
 
-1. Call [`createOsdUrlTracker()`](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/opensearch_dashboards_utils/public/state_management/url/osd_url_tracker.ts) in the set up function within public/plugin.ts 
+1. Call [`createOsdUrlTracker()`](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/opensearch_dashboards_utils/public/state_management/url/osd_url_tracker.ts) in the set up function within public/plugin.ts. The two functions that get returned, `appMounted()` and `appUnMounted()`, help with global data persistence across the app. When user enters one app, `appMounted()` will be called to make sure that the current app is actively listening to history changes. It will also initialize the URL to be previously stored URL from storage. When user leaves one app, `appUnmounted()` will be called so the app will stop listening actively on history changes, but start subscribing to the global states. Therefore, if the global states are changed in another app, the global state listener will still be triggered in this app even though it is not currently active. It will also update the corresponding URL in the browser storage. By using `appMounted()` and `appUnMounted()`, it makes sure that global data are always persisted no matter which app we are currently on.
     * declare two private variables: `appStateUpdater` observable and `stopUrlTracking()`
     ```ts
     private appStateUpdater = new BehaviorSubject<AppUpdater>(() => ({}));
@@ -68,7 +69,7 @@ For example, we set a specific time range and time refresh interval when trying
     ```
 
 3. Syncing query state with URL in public/app.tsx
-    * import `syncQueryStateWithUrl` from data plugin and call it with query service and osdUrlStateStorage service that we set in step 2
+    * import [`syncQueryStateWithUrl`](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/plugins/data/public/query/state_sync/sync_state_with_url.ts#L48) from data plugin and call it with query service and osdUrlStateStorage service that we set in step 2. This function completes two jobs: 1. When we first enter the app and there is no data stored in the URL, it initializes the URL by putting the `_g` key followed by default data values. 2. When we refresh the page, this function is responsible to retrive the stored states in the URL, and apply them to the app.
 
     ```ts
     export const VisBuilderApp = () => {